Injured Fluoro-Jade-positive hippocampal neurons contain high levels of zinc after traumatic brain injury

Abstract

Hippocampal damage contributes to cognitive dysfunction after traumatic brain injury (TBI). We previously showed that Fluoro-Jade, a fluorescent stain that labels injured, degenerating brain neurons, quantifies the extent of hippocampal injury after experimental fluid percussion TBI in rats. Coincidentally, we observed that injured neurons in the rat hippocampus also stained with Newport Green, a fluorescent dye specific for free ionic zinc. Here, we show that, regardless of injury severity or therapeutic intervention, the post-TBI population of injured neurons in rat hippocampal subfields CA1, CA3 and dentate gyrus is indistinguishable, both in numbers and anatomical distribution, from the population of neurons containing high levels of zinc. Treatment with lamotrigine, which inhibits presynaptic release of glutamate and presumably zinc that is co-localized with glutamate, reduced numbers of Fluoro-Jade-positive and Newport Green-positive neurons equally as did treatment with nicardipine, which blocks voltage-gated calcium channels through which zinc enters neurons. To confirm using molecular techniques that Fluoro-Jade and Newport Green-positive neurons are equivalent populations, we isolated total RNA from 25 Fluoro-Jade-positive and 25 Newport Green-positive pyramidal neurons obtained by laser capture microdissection (LCM) from the CA3 subfield, linearly amplified the mRNA and used quantitative ribonuclease protection analysis to demonstrate similar expression of mRNA for selected TBI-induced genes. Our data suggest that therapeutic interventions aimed at reducing neurotoxic zinc levels after TBI may reduce hippocampal neuronal injury.

Long-Lasting Suppression of Acoustic Startle Response after Mild Traumatic Brain Injury

“…32 The present study used stereology to estimate the number of degenerating cells (Fluoro-Jade positive) in the cortex and hippocampus after mTBI. Our estimates of degenerating hippocampal cells are similar to estimates obtained from stereology after mTBI using LFP 33 or to estimates extrapolated from actual Fluoro-Jade cell counts after CCI mTBI. 34 In the cortex, our estimates of degenerating cells were much less than those reported after slightly higher impact pressures (24 psi) using LFP.…”

Rapid Accumulation of Endogenous Tau Oligomers in a Rat Model of Traumatic Brain Injury

“…In our model of fluid percussion TBI, we have detected neuronal cell death as early as 4 h after TBI and do not normally see more than one or two injured neurons in the hippocampus of sham-injured animals (31,32). Tau oligomers may well be a valuable diagnostic biomarker and therapeutic target for TBI.…”

Traumatic brain injury: Can the consequences be stopped?

“…67,68 Further evidence supporting the hypothesis that there is a reduction of GluR2 following traumatic brain injury is the marked elevation in free ionic zinc in neurons following experimental brain trauma. [74][75][76] Free zinc is taken up by mitochondria in an effort to restore zinc homeostasis but, similar to the effects of mitochondrial calcium uptake, this leads to potent mitochondrial dysfunction, prolonged loss of mitochondrial membrane potential and free radical generation. 77,78 This further implicates the loss of GluR2 as an important step in neuronal death and damage.…”